Generator of square synchronizing pulses



y 1, 1954 F. A. HESTER 2,678,352

GENERATOR OF SQUARE SYNCHRONIZING PULSES Filed March 17, 1950 2 Sheets-Sheet 1 A-C POWER SOURCE SQUARE FIG-I. WAVE GENERATOR UTILIZATION MEANS 0 28 SWITCH n I I I I 1 l l E E i I z I l l I l I l- I I I l I I l I l l I i I I I l l I I I INVENTOR. o 1 2 a "'4 FRANK A.HESTER TIME y ATTORNEY May 11, 1954 Filed March 17, 1950 F. A. HESTE R GENERATOR OF SQUARE SYNCHRONIZING PULSES Sheets-Sheet 2 H PowER souRcE T 0 6 PHASE- SHIFT cm.

45 35 II 0 SQUARE SQUARE WAVE wAvE GENERATOR GENERATOR UTILIZATION MEANS FIG.4.

45 4 I I i 61 I ,3 I SWITCH I TI 14-33 *2 i l OUTPUT Fl G. 5. INVENTOR.

FRANK A. HESTER BY I ATTORNEY Patented May 11, 1954 I i A 2,678,352

GENERATOR OF SQUARE SYNCHRONIZIN G PULSES Frank A. Hester, New York, N. Y., assignor to Faximile, Inc., New York, N. Y., a corporation of Delaware Application March 17, 1950, Serial No. 150,181

Claims. (Cl. 178-695) The present invention concerns synchronizing of mechanical equipment and, in particular, methods of and means for generating accurately shaped and timed synchronizing impulses.

This application is a continuation-in-part of co-pending application Serial No. 710,030, filed on November 15, 1946.

In many types of equipment, pulses of definite size and shape must be transmitted at predeter mined regular or. irregular intervals to control the speed or position of other components of the system. In facsimile apparatus, for instance, one means by which recorder and transmitter motors may be properly framed and kept in syn-. chronism requires the transmission of a square wave impulse during a certain portion of each revolution ofv the transmitter scanner drum, which is used to operate synchronizing and/or framing circuits at the recorder. In order to in sure positive action from such a device, the framing impulse must be substantially square and of predetermined width, and in addition, it must be accurately timed and positioned. One method commonly employed for generating such a framing impulse has been a commutator mounted on the scanner drum shaft to generate animpulse; during the time between succeeding scanned lines. With this system it has been found that frequently faulty contact is obtained due to a mechanical failure where dirty contact surfaces and other mechanical conditions result in a ragged, irregular and generally unsatisfactory synchronizing impulse. When such a faulty impulse is utilized to synchronize the receiving scanner, inaccuracies result in the framing and synchronizing which cause the recorded copy to follow an irregular path.

According to the present invention various synchronizing impulses are generated electrically which have the desired accuracy of shapeand timing and the commutator or similar device. 0p-

erated by the transmitting scanner merely selects every nth pulse. The selection is carried out in such a manner that it does not aifect any characteristic of the synchronizing impulse and, hence, the transmitted impulse has all the .desired characteristics for such a system. While the commutator or similar contact acts as a switch to allow the synchronizing impulse to be passed on to a utilization circuit, the synchronizing impulse does not pass through the commutator and its shape and timing is independent of the commutator operation even though an imperfect contact may be made. Thus the faults inherent in the mechanical commutator system for generating an impulse are entirely eliminated and highly accurate and stable synchronizing impulses are transmitted to the equipment to be controlled.

It is therefore an object of the present invention to provide means for generating periodic pulses which are accurately spaced in time and which are synchronized with a rotating mechanical equipment.

It is another object to provide synchronizing pulse generating means wherein imperfect brush and commutatorcontact does not adversely affect the accuracy and spacing of the pulses.

Pursuant to these and other objects which will be apparent to those skilled in the art, there is provided a mechanical, selector switch which is driven by a synchronous motor supplied from an A.-C. source. A square wave generator supplied from the same A.-C. source converts the sine wave alternating current into a square wave alternating current, the output of the generator being connected to the plate of a thyratron tube. By reason of the common A.-C. source, the mechanical selector switch and the square wave generator operate in synchronism. The switch is closed for a duration in the order of the dura' tion of one-half cycle of the square wave signal, and the repetition rate of .the switch cycle is N l/nth the frequency of the square wave signal.

The selector switch is used to actuate a storage circuit which in turn, controls the bias on the thyratron so that only every nth square wave positive half cycle is allowed to pass through the thyratron to generate an output pulse. In one embodiment of the invention the storage circuit includes a capacitor, and in a second embodiment the storage circuit includes a second synchronized square wave generator and a sec 0nd thyratron.

"Referring briefly to the drawings:

Fig. 1 is a diagram of a facsimile synchronizing signal generator constructed according to the teaching of the invention.

Fig. 2 is a representation of waveforms which will be used in explaining the operation of the Fig. l embodiment.

Fig. 3 is a representative chart of voltage vs.

time on the storage circuit of the Fig. 1 embodiment.

Fig. 4 is a diagram of a second embodiment of the invention.

Fig. 5 is a representation of waveforms which" 4 3 of the drawings, an A.C. power source It supplies a synchronous motor or gearmotor l l which drives a facsimile copy drum l2 and a commutator [3. The commutator it has a single contact segment M oriented on the common shaft in an angular position between the ends of the copy 1.6 wrapped around copy drum i2. A photocellpickup ii is engaged .with'airotatirig lead screw i8 which slowly moves the pickup along the length of copy drum !2. Each time the copy drum makes one revolution, a single line of the copy i 6 is translated'intoan electrical signal. According to this. invention, an accurately shaped and timed pulse is generated betweenaeach line of copy for transmission;along with ,theJfacsimile signal to provide synchronous operation of facsimile recorders receivingthe signal.

A thyratron has any suitable electrode ar rangement such as a cathode 2i heated hyconventional means not shown, a screen or suppres sorgrid 22, a-plate 23,.and an ionization con-- trolelectrode 24. An output =loadresistor :28 !is connected between cathode 2i and ground, and a utilization means 21 is connected acrossresistor.2.5. CathodeZi vis biased-positiverelative to groundbymeans of battery 28 connected across resistors 29 audit acting as a voltage divider. A storage circuit comprising a capacitor 30 shunted by resistor 3| is connectedbetweencon trol electrode.2-A and ground. .A control bias battery 32 is connected on.-its negativeside to. ground and .on its positive side through brushes 33 to control electrode .24. Thecircuit betweenbrushes 33 .is periodically closed .by contact segment 14 as commutator l3 rotates.

A square .wavegenerator 35 is supplied from A.-C.,power source 10 and its output is connected across, plate 230i thyratron 2i and ground. Generator L35 isof the commontype having-an output synchronized with the input power and preferablyis a limiter which squares up the sine wave input.

Fig.2 shows the relationship betweentheoutput of the generator.35 and the closed circuit condition of switch i l-43. Since the synchro nous motor Hand the generator .35 are supplied from .the .same source it, the generator and switch operateinsynchronisni. Thephase displacement of the. switch operation relative tothe generator output is determined by the angular position otcommutator 43 on shaft i5. This displacementis selected so that the switch 14-43 isclosed from a time during the negative half cycle of the generator output to a timeduring thefollowing positive half cycle of the generator output. .The output pulsesgenerated across load resistor ztcorrespond in duration .to generator pulses 36.

By way of example, if the A.-C. power source H3 is 60 cycles .persecond, andtheoutput of the generatorfil'i is 60 cycles per second, andthe drum l,2.and commutator [3 are run at 360 revolutions per minute or 6 revolutions per secondthe switch Ill-33 will be closed once per every n cyclesin the generator output, n being 10. The width of each positive half cycleinthe generator output will be 18 degrees in relation to the .360 degrees of angular displacement of drum 1? during onerevolution.

The bias on cathode 2! of thyratron 28 is such that positive pulses applied from generator 3'5 to plate 23 will not fire the thyrat-ron unless a predetermined positive control bias E2 is applied to the control electrode. A greater "positive voltage E1 is appliedto control electrode-24 from :may be as :representedin .Fig..3-.where the control bias from battery 32 is shown as E1. Contact across brushes 33 is made from time To to T1, momentarily at time T2, and from time T3 to T4. 'The-'contact-isinterrupted from time T1 to *T2, from time T2 to T3 and from time T4 on, these interruptions being due to faulty contact of brushes 5 -33 2011 :segment Hi. When contact is made, capacitor wis charged to voltage E1, and when -contact .is interrupted, capacitor 3!! discharges through resistor 3l, the components being-selected to provide a time constant such that the control bias voltage is reduced below the minimum firingbias voltage E2 prior to the -appearanceon. plate 23 of the next succeedingpositive half cyclelfrom. generator 35.

A positive halfcycle-applied-to plate-2.3at'any time between time To. and T5 will cause thethyratron :20 to fire andgenerate a corresponding pulse across output resistor 5. It .will be understood that Fig.3 .ismerely illustrative of the effect ofpoorelectricalcontact inswitch Ill-33. Fig.3 shows how contact occurring at anytime within a considerable period v.will bias thyratron 20 so that the next accurately .timed positive pulseapplied toplate 2.3 .willfire the tube.

Fora description of asecondembodimentof the invention, reference is now had to Fig. 4 wherein elementscorresponding .to-elements in Fig. .1 are given the same numerals. The Fig. 4 embodiment has a .dififerentstorage circuit in cluding asecondthyratron-lfl havinga cathode M, asuppressorgridfl, a plate. 43 .andacontrol electrode A4,..and a. second square wave, generator 45. Cathode 14! is connected through output resistor 45 to ground. The positive side ofbias battery lii is connected through resistors-58 and 5E) to cathodeALand the negative side isconnected .to groundand to control electrode It. When .contact vis-established :across brushes .33. junctionpoint 52 between voltagedivider resistorsda and 50 is placed at.groundpotential-thereby reducing the .bias 1 across cathode H and controlelectrode 44A sufficiently .to allow thyratron 49 v.tofire if a .positive pulse is simultaneously appliedtoplate Miromgenerator 45.

Battery 48 is also used to bias .the cathode ii of thyratron 20 by aconnection .from the posi tiveside through voltage divider resistors-29 and 26 to ground, the negative sidebeing connected directly .togroundand. through resistors 45 and di to .thecontrol electrode .24. The .biason thy-- ratronzfi such that when thyratrontfl is con ducting, the .voltagedeveloped across load resistor 46 applied to .control.electrode .24 is sufiicient to overcome the sins and allow thyratron .29 to fire on theapplication ,to plate .23 of a positive pulse from generator 35.

.Square wave generator .45 is supplied from A.-C source it through a phase shift circuit 55. .By reason .of the common .power supply, switch I l-33, generator 45am]. generator 35 all operate in synchronism and have .a phase .rela tionship approximately as shown in Fig. 5. if switch I4-33 makes contact at any time between times trend in, positivepulse 50 from generator 55 will fire 'thyratron 48 thereby conditioning thyratrontO-to fire during the time tz-to'ta' when positive pulse BI is applied from generator 35. The output voltage pulse 62 is developed across resistor 26. Output pulse 53 is accurately proportioned and timed regardless of the time when good contact is made by switch l4--33 during the period t1 to is. It will be understood that once thyratron 20 or 40 is fired by a positive pulse on its plate, it will continueto conduct until the end of the pulse and will not conduct on the succeeding pulses because of the absence of favorable cathode-control electrode bias.

It will be apparent that the embodiments of the invention shown in Figs. 1 and 4 are similar and that they differ only in the nature of the storage means connected between switch [4-33 and thyratron 20.

While only two forms of the invention have been shown and described, many variations will be apparent to those skilled in the art which are within the spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

1. In a facsimile transmitter having a rotating scanner member, means for generating a square synchronizing pulse at a time corresponding to an angular position of the scanner member cornprising a square wave generator having an output frequency in cycles per second which is n times the normal operating revolutions per second of the scanner member, where n is an integer greater than one, an electron discharge tube rcccptive to said square wave generator output, a mechanical selector switch operative synchronously with the scanner member, and a storage circuit responsive to said selector switch and operative to bias the electron discharge tube so that it will conduct upon the application thereto of every nth positive half cycle of the square wave generator.

2. In a facsimile transmitter, means for generating a square synchronizing pulse, comprising in combination, an A.-C. power source, a square wave generator operated from and synchronously with said source, a synchronous motor operated from said source, a mechanical selector switch driven by said motor, means controlled by said switch including a storage circuit for generating one pulse per n cycles of said square wave generator, where n is an integer greater than one, and an electron discharge tube including a plate circuit and a control circuit, the plate circuit being receptive .to the output of said square wave generator, and the control circuit being receptive to the output of said storage circuit, whereby the output of the electron discharge tube is a regularly-occurring square pulse substantially unaffected by the limitations of the mechanical selector switch.

3. In a facsimile transmitter, means operated from an A.-C. power source for generating a square synchronizing pulse between the signals corresponding to successive lines of graphic copy scanned, comprising in combination, a square wave generator operated from and synchronously with said source, a synchronous motor operated from said source, a mechanical selector switch driven by said motor, the selector switch being operative once for every n cycles of said generator where n is the ratio of the cycles of said source per unit of time to the lines scanned per unit of time, a storage circuit responsive to said switch, and an electron discharge tube including a plate circuit and a control circuit, the plate circuit being receptive to the output of said generator, and the control circuit being receptive to the output of said storage circuit, whereby the output of the electron discharge tube is a regularly-occurring synchronized square pulse.

4. A generator of square synchronizing pulses comprising in combination, an A.-C. power source, a square wave generator operated from and synchronously with said source, a synchronous motor operated from said source, a selector switch driven by said motor, means controlled by said switch including a storage circuit for generating one pulse per 11. cycles of said square wave generator and a control device receptive to the output of said square wave generator, said control device including a control circuit receptive to the output of the storage circuit whereby the output of the control device is a regularly occurring substantially square synchronizing pulse.

5. A generator of square synchronizing pulses comprising in combination a square wave generator operable from and in synchronism with an A.-C. source, a synchronous motor operable from said A.-C. source, a selector switch driven by said motor,'the' selector switch being operative once for every 11. cycles of said square wave generator where n is an integer greater than one, a storage circuit responsive to said switch, and a control device receptive to the output of said square wave generator, said control device including a control circuit receptive to the output of said storage circuit, whereby the output of the control device is a regularly occurring substantially square synchronizing pulse.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,326,740 Artzt Aug. 17, 1943 2,496,543 Kanncr Feb. '7, 1950 2,512,647 Hester June 1'7, 1950 2,530,516 Finch Nov. 21, 1950 2,532,576 Sherwin et a1. Dec. 5, 1950 

